Steam turbines extract work from steam to generate power. A typical steam turbine may include a rotor associated with a number of wheels. The wheels may be spaced apart from each other along the rotor, defining a series of stages. The stages are designed to efficiently extract work from steam traveling on a flow path from an entrance to an exit of the turbine. As the steam travels along the flow path, the steam may cause the wheels to drive the rotor. The steam may gradually expand, and the temperature and pressure of the steam may gradually decrease. The steam is then exhausted from the exit of the turbine.
Higher-temperature steam turbines may generate increased output, as the increased temperature of the steam may increase the energy available for extraction in the stages. For example, a reheat steam turbine may include a high-pressure (HP) section, an intermediate pressure (IP) section, and a low-pressure (LP) section. The sections may be arranged in series with each section including stages. Within the sections, work is extracted from the steam to drive the rotor. Between the sections, the steam may be reheated to recondition the steam for performing work in the next section. The HP and IP sections may operate at relatively high temperatures, increasing the turbine output.
Although higher-temperature steam turbines may be capable of increased output, the higher-temperatures may challenge the materials used to form the turbine components. For example, the rotor may include a series of integral dovetails that permit joining buckets to the wheels. At higher temperatures, the attachment area of the dovetail and the bucket may experience stress, risking creep or failure. One solution may be to form the rotor and associated dovetails from materials selected to withstand higher temperatures. However, such materials tend to be relatively expensive and may be relatively difficult to manufacture in the desired geometry. Another solution may be to cool the attachment area using steam that is externally routed to the attachment area. However, such steam has not performed work elsewhere in the turbine, and therefore employing such steam for cooling purposes is inefficient and may cause performance losses. From the above, it is apparent that a need exists for systems and methods of cooling the wheel of a steam turbine, and more specifically the attachment area at which the wheel is joined to the rotor.